Hydraulic pump

ABSTRACT

A hydraulic pump includes a cylinder block having a cylinder, a rotor rotatable in the cylinder, and a vane movable in a radial direction of the rotor and biased to the rotor. The vane, the cylinder, and the rotor thereamong define an operation chamber. The rotor draws fluid into the operation chamber and sends the fluid outside the operation chamber. The vane is urged to the rotor according to differential pressure between pressure of fluid at high-pressure in the operation chamber and pressure of fluid at low-pressure in the operation chamber. The vane and the rotor define a hardness ratio being calculated by dividing hardness of the vane by hardness of the rotor, and the hardness ratio is greater than or equal to 1.6.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by referenceJapanese Patent Application No. 2007-91582 filed on Mar. 30, 2007.

FIELD OF THE INVENTION

The present invention relates to a hydraulic pump. In particular, thepresent invention may relate to a refrigerant pump for pumpingrefrigerant fluid to a heater in a waste heat recovery system such as aRankine cycle system.

BACKGROUND OF THE INVENTION

For example, JP-A-63-277883 discloses a rotary compressor configured tobe provided to an airconditioner, a refrigerator, or the like. In thepresent rotary compressor, a vane is provided to a cylinderaccommodating a rotor. The vane is movable in a vane groove provided inthe cylinder. The vane has a tip end urged to a rotor and the tip end ofthe vane is formed from a material being excellent in wear resistancecompared with that of a body portion of the vane. In the presentstructure, the tip end of the vane is enhanced in wear resistance, andabrasion caused in a wall surface, which defines the vane groove, isreduced.

The rotary compressor is configured to compress vapor-phase refrigerantin a refrigeration cycle of, for example, an airconditioner. In thepresent structure, the vane and the rotor are capable of therebetweensufficiently forming an oil film in a steady operation, therebymaintaining therebetween a state of fluid lubrication. In the presentstructure, only in a transitional operation at the time of starting orstopping of the operation of the rotary compressor, the vane and therotor are in a state of boundary lubrication where the vane and therotor therebetween do not sufficiently form an oil film. Therefore, asindicated by a dashed line in FIG. 6, development in abrasionaccompanying time progress is not so significant in the rotarycompressor. Therefore, in the rotary compressor, wear resistance needsto be considered only in the state of boundary lubrication.

However, in a hydraulic pump, which pumps low-viscosity fluid, a vaneand a rotor are regularly in the state of boundary lubrication at anyoperations. Therefore, as indicated by a solid line in FIG. 6, the vaneand the rotor are apt to therebetween significantly develop abrasionaccompanying time progress. Accordingly, only the above structure of therotary compressor, in which the tip end of the vane is formed from thewear-resistive material, may not be practical for reducing abreaction inthe hydraulic pump configured to pump low-viscosity fluid.

As follows, an exemplified premise for calculating a minimum oil filmthickness t and an oil film parameter Λ is described with reference toFIG. 7. In the present premise, fluid fed by the hydraulic pump hasviscosity of 1 [mPa·s], a vane 151 has a tip radius Rv of 20 [mm], thevane 151 exerts load F of 4000 [N/m] per unit length to a rotor 141, thevane 151 has surface roughness Rzv of 0.8, the rotor 141 has radius Rrof 20 [mm], the rotor 141 slides at sliding speed v of 1 [mm/s], and therotor 141 has surface roughness Rzr of 0.32.

According to the premise and the elastohydrodynamic lubrication theory,the minimum oil film thickness t between the vane 151 and the rotor 141and the oil film parameter Λ are calculated such that the minimum oilfilm thickness=0.03 [μm] and the oil film parameter Λ<1. According tothe calculation, the vane 151 and the rotor 141 are obviously in thestate of boundary lubrication in the hydraulic pump. Therefore, abrasionbetween the vane 151 and the rotor 141 in the hydraulic pump needs to besteadily suppressed so as to enhance product lives of both the vane andthe rotor and maintain a performance of the hydraulic pump for a longperiod.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, it is an object of thepresent invention to produce a hydraulic pump having a vane and a rotorfor pumping liquid-phase fluid, the hydraulic pump being capable ofrestricting ablation between the vane and the rotor and capable ofmaintaining a performance thereof.

According to one aspect of the present invention, a hydraulic pumpcomprises a cylinder block having a cylinder. The hydraulic pump furthercomprises a rotor rotatable in the cylinder. The hydraulic pump furthercomprises a vane movable substantially in a radial direction of therotor and configured to be biased to the rotor. The vane, the cylinder,and the rotor thereamong define an operation chamber. The rotor isconfigured to draw fluid into the operation chamber and configured tosend the fluid outside the operation chamber. The vane is configured tobe urged to the rotor according to differential pressure betweenpressure of fluid at high-pressure in the operation chamber and pressureof fluid at low-pressure in the operation chamber. The vane and therotor define a hardness ratio being calculated by dividing hardness ofthe vane by hardness of the rotor. The hardness ratio is greater than orequal to 1.6.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a sectional view showing a hydraulic pump according to a firstembodiment;

FIG. 2 is a sectional view taken along the line II-II in FIG. 1;

FIG. 3 is an enlarged sectional view showing a vane, a rotor, andperipheral components of the hydraulic pump;

FIG. 4 is a schematic view showing an ablation developed in the vane;

FIG. 5 is a table showing specific wear rates of both the vane and therotor of the hydraulic pump;

FIG. 6 is a graph showing a relationship between ablation, which isdeveloped in each of a rotary compressor and a hydraulic pump, and anoperation period; and

FIG. 7 is a schematic view showing a vane and a rotor being in contactwith each other.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

In the present embodiment, a refrigerant pump 100 is provided to pumpliquid-phase refrigerant as fluid in a Rankine cycle for recovery ofwaste heat. The Rankine cycle as a waste heat recovery cycle is, forexample, provided to a vehicle. Next, a structure of the refrigerantpump 100 is described with reference to FIGS. 1, 2. The waste-heatrecovery Rankine cycle is constructed by combining the refrigerant pump100, a heater, an expansion device, and a condenser to define an annualcircuit. The condenser condenses therein liquid-phase refrigerant, andthe refrigerant pump 100 feeds the condensed refrigerant to the heater.The heater heats the liquid-phase refrigerant using waste heat of aninternal combustion engine of the vehicle. The liquid-phase refrigerantin the heater is heated to be superheated steam refrigerant. Thesuperheated steam refrigerant is fed into the expansion device, wherebythe expansion device recovers kinetic energy caused by expansion of thesuperheated steam refrigerant. The refrigerant used in the presentwaste-heat recovery Rankine cycle is preferably used for a refrigerationcycle of an airconditioner of the vehicle.

The refrigerant pump 100 is a rotary-vane pump having a cylinder, whichaccommodates a rotor and a vane. In the present embodiment, therefrigerant pump 100 is a two-cylinder pump having two cylinders 121,two rotors 141, and two vanes 151.

The refrigerant pump 100 has a body portion, which is constructed bycombining a side plate 111, one cylinder plate 120, an intermediateplate 112, another cylinder plate 120, a side plate 113, and a bearingholder 114 in order. Each of the components of the body portion of therefrigerant pump 100 is substantially in a flat cylinder shape.

The side plate 111 has one-end side on the left side in FIG. 1, and theone-end side has a large opening being configured to be mounted with anadditional device such as an electric motor as a driving source of therefrigerant pump 100. The opening in the one-end side of the side plate111 is reduced in diameter stepwise toward the other-end side on theright side in FIG. 1, whereby the opening is communicated with theother-end side of the side plate 111. The other-end side of the sideplate 111 has a communication hole having an inner diameter, which isless than an inner diameter of the cylinder 121 of the cylinder plate120. The communication hole of the other-end side of the side plate 111is inserted with a shaft 131. The other-end side of the side plate 111has a center portion fixed with a bearing 133. The bearing 133 rotatablysupports one-end of the shaft 131.

The intermediate plate 112 and the side plate 113 are disc-shapedmembers respectively having center portions defining insertion holes.The insertion holes of the intermediate plate 112 and the side plate 113are substantially the same as the opening of the side plate 111 on theother-end side in inner diameter. The bearing holder 114 is a bottomedcylindrical member having a center portion defining a recess on theone-end side. The recess of the bearing holder 114 is provided with abearing 134, which rotatably supports the other-end side of the shaft131.

Each cylinder plate 120 is a cylinder block member being in a discshape. The cylinder plate 120 has a center portion defining the cylinder121 being in a circular shape. One of the cylinder plates 120 isinterposed between the side plate 111 and the intermediate plate 112.The other cylinder plate 120 is interposed between the intermediateplate 112 and the side plate 113. The side plate 111, the one cylinderplate 120, the intermediate plate 112, the other cylinder plate 120, theside plate 113, and the bearing holder 114 are communicated with eachother through the insertion hole and the cylinders 121.

Each cylinder plate 120 has an inlet port 122, an outlet port 123, avane groove 124, and a backpressure feed port 125, in addition to thecylinder 121. In the present structure, the inlet port 122 as onecommunicating portion is provided for communicating an exterior of thecylinder plate 120 with an interior of the cylinder 121. The outlet port123 as another communicating portion is provided for communicating theinterior of the cylinder 121 with the exterior of the cylinder plate120. The outlet port 123 is adjacent to the inlet port 122 with respectto a circumferential direction of the cylinder plate 120. The vanegroove 124 extends from the cylinder 121 radially outward in thecylinder plate 120. The vane groove 124 is located circumferentiallybetween the inlet port 122 and the outlet port 123. The backpressurefeed port 125 as another communicating portion is provided forcommunicating an interior of the vane groove 124 with a high-pressurechamber in an operation chamber V.

The shaft 131 has two portions correspondingly to the two cylinders 121,and each of the two portions of the shaft 131 is provided with acircular cam portion 132. The circular cam portion 132 is eccentricrelative to an axis of the shaft 131.

The rotor 141 is a flat cylindrical member and rotatably equipped to anouter circumferential periphery of the cam portion 132 via a bearing(not shown) for feeding liquid-phase refrigerant. An outer diameter ofthe rotor 141 is smaller than an inner diameter of the cylinder 121. Therotor 141 is inserted into the cylinder 121 such that the rotor 141 isconfigured to revolve around the cam portion 132 in the cylinder 121.

The vane 151 is a plate-shaped member and accommodated in the vanegroove 124 such that the vane 151 is movable in the vane groove 124. Aspring 152 is interposed between a recess in a bottom of the vane groove124 and the vane 151. The spring 152 biases the vane 151 toward therotor 141 such that a tip end of the vane 151 is in contact with anouter circumferential periphery of the rotor 141 mainly in a conditionwhere the refrigerant pump 100 stops. The rotor 141 and the vane 151define the operation chamber V in the cylinder 121.

Here, hardness of a material of each of the vane 151 and the rotor 141is predetermined by selecting a material of each of the vane 151 and therotor 141 and selecting heat treatment applied to the material. Morespecifically, a hardness ratio Hr between hardness Hvv of the vane 151and hardness Hvr of the rotor 141 is predetermined to be greater than orequal to 1.6. Here, the hardness ratio Hr is defined by dividing thehardness Hvv of the vane 151 by the hardness Hvr of the rotor 141.

The refrigerant pump 100 with the structure described above has theinlet port 122 and the outlet port 123. The inlet port 122 is connectedwith an outlet of the condenser, and the outlet port 123 is connectedwith an inlet side of the heater. When an electric motor (not shown) asa driving source drives the shaft 131, each rotor 141 revolves aroundthe cam portion 132 in the cylinder 121, whereby the rotor 141 drawsliquid-phase refrigerant from the condenser into the operation chamber Vand pumps the liquid-phase refrigerant to the heater.

In this operation, the high-pressure chamber in the operation chamber Vis communicated with the vane groove 124 through the backpressure feedport 125, so that urging force is exerted to the vane 151 to urge thevane 151 onto the rotor 141 correspondingly to differential pressurebetween pressure in the low-pressure chamber and pressure in thehigh-pressure chamber. The urging force is steadily applied to the vane151 to bias the vane 151 toward the rotor 141, so that a tip end of thevane 151 is steadily maintained in contact with the outercircumferential periphery of the rotor 141. In the present structure,the vane 151 is maintained in contact with the rotor 141, wherebyliquid-phase refrigerant in the high-pressure chamber can be restrictedfrom leaking into the low-pressure chamber.

Next, the urging force exerted to the vane 151 is further specificallydescribed with reference to FIG. 3. Here, the spring 152 is provided inthe vane groove 124. The spring 152 exerts biasing force to the vane 151to maintain the state where the vane 151 is in contact with the rotor141 mainly in a state where the refrigerant pump 100 stops. In thisstructure, the spring 152 biases the vane 151 to restrict liquid-phaserefrigerant in the high-pressure chamber from leaking into thelow-pressure chamber when the refrigerant pump 100 starts operation. Thebiasing force of the spring 152 is significantly small and negligiblecompared with the urging force, which correlates with the differentialpressure between the high-pressure chamber and the low-pressure chamber.Therefore, in the following description, the biasing force of the spring152 is disregarded.

In FIG. 3, a thickness direction of the vane 151 is defined as ahorizontal direction (left and right direction), and a directionperpendicular to the sheet of FIG. 3 is defined as a depth direction ofthe vane 151. The operation chamber V on the right side of the vane 151is a low-pressure chamber directly communicating with the inlet port122. The operation chamber V on the left side of the vane 151 is ahigh-pressure chamber directly communicating with the outlet port 123.

In an initial state, the tip end of the vane 151 is substantially inconvex. The tip end has a center portion with respect to the thicknessdirection, and the center portion has the maximum projected portionrelative to the rotor 141. The tip end of the vane 151 and the rotor 141therebetween have a contact portion in which the tip end of the vane 151defines a contact point 151 a. The contact point 151 a is at a distanceLhigh from an end of the vane 151 on the high-pressure side, i.e., onthe side of the high-pressure chamber. The contact point 151 a is at adistance Llow from an end of the vane 151 on the low-pressure side,i.e., on the side of the low-pressure chamber. Backpressure Pb isapplied to the vane 151 toward the rotor 141. The high-pressure chamberis at pressure Phigh. The low-pressure chamber is at pressure Plow.

The vane 151 has a depth DP with respect to the depth directionorthogonal to the page of FIG. 3. The vane 151 is exerted with backpressure force Fb, which is calculated by the following equation 1.

Fb=Pb×(Lhigh+Llow)×DP  (1)

The vane 151 is also exerted with pushback force Fhigh from thehigh-pressure chamber.

Fhigh=Phigh×Lhigh×DP  (2)

The vane 151 is further exerted with pushback force Flow from thelow-pressure chamber.

Flow=Plow×Llow×DP  (3)

Here, the backpressure Pb is equal to the pressure Phigh, and accordingto the above equations (1) to (3), urging force Fu, with which the vane151 is exerted toward the rotor 141, can be calculated by the followingequation (4).

Fu=Fb−(Fhigh+Flow)=(Phigh−Plow)×Llow×DP  (4)

Thus, the urging force Fu is determined correspondingly to thedifference between the pressure Phigh in the high-pressure chamber andpressure Plow in the low-pressure chamber. The urging force Fu becomeslarge as the distance Llow increases.

As an operation period of the refrigerant pump 100 increases, abrasionbetween the vane 151 and the rotor 141 develops. Specifically, as shownin FIG. 4, the convex portion of the tip end of the vane 151 is scrapedsubstantially to be a flat surface extending along an envelope definedby revolution of the rotor 141. In the initial state, the tip end of thevane 151 is in contact with the rotor 141 via a contact surface of acontact width A. As the vane 151 is scraped and worn out as the rotor141 revolves, the contact width A increases to a contact width B.Therefore, at a time point in the operation of the refrigerant pump 100,the contact point 151 a largely moves toward the low-pressure chamber,and the distance Llow decreases. As a result, the urging force Fuexerted to the vane 151 decreases. Consequently, liquid-phaserefrigerant may leak from the high-pressure chamber into thelow-pressure chamber, and such leakage results in decrease in a pumpperformance of the refrigerant pump 100. In addition, the vane 151 mayfluctuates to cause further ablation, breakage in the components, andabnormal noise between components.

Therefore, in the present embodiment, the hardness ratio Hr is definedby the value of: (hardness Hvv of the vane 151)/(the hardness Hvr of therotor 141), and the hardness ratio Hr is determined to be greater thanor equal to 1.6. In the present structure, ablation between the vane 151and the rotor 141 can be steadily reduced.

Specifically in the present embodiment, as shown in FIG. 5, the basematerial of the vane 151 is selected from four kinds of tool steelincluding chrome molybdenum steel (SCM415), high-speed tool steel(SKH51), and alloy tool steel (SKD11). The surface of the vane 151 isapplied with heat treatment including carburizing, quenching, andtempering (GC), softnitriding (TFG) with quenching and tempering (QT),chromium nitride coating (CrN), and titanium nitride coating (TiN).Surface roughness Rz of the vane 151 is predetermined to 3.2 or 0.3.

Here, the surface roughness Rz is, for example, a ten points averageheight as mean roughness depth calculated by measuring distances betweenhighest five peaks and lowest five bottoms, then averaging thedistances.

In the present embodiment, the base material of the rotor 141 is chromemolybdenum steel (SCM415) as case-hardened steel. The surface of therotor 141 is applied with carburizing, quenching, and tempering (GC).Surface roughness Rz of the rotor 141 is predetermined to 3.2.

Vickers hardness (Hv) of each material applied with heat-treating isobtained. The hardness ratio Hr is defined by the following equation (5)using hardness Hvv of the vane 151 and hardness Hvr of the rotor 141.

Hr=Hvv/Hvr  (5)

A specific wear rate WR [m2/N] of each of the vane 151 and the rotor 141is defined by the following equation (6) using abrasion ABR [m3], load L[N], and sliding distance D [m].

WR[m2/N]=ABR[m3]/L[N]×D[m]  (6)

As shown in FIG. 5, a result indicating the specific wear rate WR ofeach of the vane 151 and the rotor 141 relative to each hardness ratiosHr is obtained by combining relations between the materials, the heattreatment, and the surface roughness Rz of the vane 151 and the rotor141 at four levels. According to the result, as the hardness ratio Hrincreases, the specific wear rate WR of the vane 151 substantiallydecreases, and the specific wear rate WR of the rotor 141 substantiallyincreases. It suffice to determine the hardness ratio Hr to be greaterthan or equal to 1.6 so as to restrict the specific wear rate WR of thevane 151 to be less than the specific wear rate WR of the rotor 141.

It is confirmed in advance that it suffices to restrict the specificwear rate WR of each of the vane 151 and the rotor 141 to be less thanor equal to about 10 to the minus 16th power [m2/N] so as to restrictleakage of liquid-phase refrigerant. To satisfy the present condition ofthe specific wear rate WR, it suffice to restrict the hardness ratio Hrto be less than or equal to about 2.5. Thus, according to the resultshown in FIG. 5, both the levels 2, 3 are determined to be preferable.

As described above, the specific wear rate WR of the vane 151 relativeto the rotor 141 can be steadily suppressed by determining the hardnessratio Hr between the vane 151 and the rotor 141 to be greater than orequal to 1.6. Therefore, by determining the hardness ratio Hr to begreater than or equal to 1.6, the contact width of the vane 151 relativeto the rotor 141 can be restricted from increasing. Thereby, the contactpoint between the vane 151 and the rotor 141 can be restricted frommoving toward the low-pressure chamber as described above with referenceto FIG. 4. Thus, the pump performance of the refrigerant pump 100 can bemaintained for a long period. The specific wear rate WR of, inparticular, the rotor 141 can be suppressed by determining the hardnessratio Hr to be less than or equal to 2.5, and the pump performance ofthe refrigerant pump 100 can be significantly maintained.

Second Embodiment

The specific wear rates WR of the vane 151 and the rotor 141 can befurther reduced by appropriately determining the surface roughness Rz ofthe vane 151 and the rotor 141, in addition to the determination in thefirst embodiment.

According to the first embodiment, when the surface roughness Rz of therotor 141 is reduced from 3.2 to 0.08 in the level 2 in FIG. 5, thespecific wear rate WR of the vane 151 can be reduced to a value of8.63×10 to the minus 19th power [m2/N], and the specific wear rate WR ofthe rotor 141 can be reduced to 2.22×10 to the minus 18th power [m2/N].In the present determination of the surface roughness Rz of the rotor141, the specific wear rate WR of the vane 151 is reduced by two ordersof magnitude, and the specific wear rate WR of the rotor 141 is reducedby one order of magnitude. The specific wear rate WR is considered to bepresently reduced, since abrasion between the vane 151 and the rotor 141is reduced by the determination of the surface roughness Rz of the rotor141.

Therefore, it suffices to determine the surface roughness Rz of the vane151 to be less than or equal to 0.3 and the surface roughness Rz of therotor 141 to be less than or equal to 0.1 so as to reduce the specificwear rates WR of both the vane 151 and the rotor 141 to be less than orequal to 10 to the minus 18th power [m2/N].

Other Embodiments

In the first embodiment, the above structure is applied to therefrigerant pump 100 for the waste-heat recovery Rankine cycle providedto the vehicle. Alternatively, the above structure may be applied tovarious hydraulic pumps for pumping fluid. For example, the abovestructure may be applied to a hydraulic pump for a Rankine cycleprovided to a stationary power generator or the like.

Various modifications and alternations may be diversely made to theabove embodiments without departing from the spirit of the presentinvention.

1. A hydraulic pump comprising: a cylinder block having a cylinder; arotor rotatable in the cylinder; and a vane movable substantially in aradial direction of the rotor and configured to be biased to the rotor;wherein the vane, the cylinder, and the rotor thereamong define anoperation chamber, the rotor is configured to draw fluid into theoperation chamber and configured to send the fluid outside the operationchamber, the vane is configured to be urged to the rotor according todifferential pressure between pressure of fluid at high-pressure in theoperation chamber and pressure of fluid at low-pressure in the operationchamber, the vane and the rotor define a hardness ratio being calculatedby dividing hardness of the vane by hardness of the rotor, and thehardness ratio is greater than or equal to 1.6.
 2. The hydraulic pumpaccording to claim 1, wherein the hardness ratio is less than or equalto 2.5.
 3. The hydraulic pump according to claim 1, wherein the vane isformed from tool steel being quenched and tempered, and the rotor isformed from case-hardened steel being carburized, quenched, andtempered.
 4. The hydraulic pump according to claim 3, wherein the vaneis formed from the tool steel nitrided after being carburized, quenched,and tempered.
 5. The hydraulic pump according to claim 1, wherein thevane and the rotor therebetween define a sliding portion, in which: asurface roughness Rz of the vane is equal to or less than 0.3, and asurface roughness Rz of the rotor is equal to or less than 0.1.
 6. Thehydraulic pump according to claim 1, the hydraulic pump being used for avehicle.
 7. The hydraulic pump according to claim 6, the hydraulic pumpbeing used for a waste heat recovery cycle for the vehicle.
 8. Thehydraulic pump according to claim 7, wherein the waste heat recoverycycle is a Rankine cycle.